Certain techniques for planning orthopedic surgical procedures involve utilizing patient-specific information, such as a model of a bone, to accurately determine various parameters for a customized surgical procedure and/or customized orthopedic implant. Such techniques may involve determining an optimal orientation of the bone model based on one or more axes of the bone model. For example, a technique for planning a knee replacement procedure may include determining the optimal orientation of a distal femur model based on the anterior-posterior (AP) axis, the transepicondylar axis (TEA), and/or the posterior condylar axis (PCA).
One metric that is widely recognized as an important predictor for the outcome of total knee replacement surgeries is the varus-valgus alignment of the knee. Due to the fact that the rotation about the AP axis determines the varus-valgus angle, accurate determination of the AP axis plays an important role in the planning process. Rotation of the model about an inaccurate AP axis may result in a flawed or sub-optimal plan, thereby leading to surgical outcomes that are less than ideal. One difficulty that may arise in the planning procedure stems from the fact that the feature points utilized in determining the AP axis are generally less well-defined than those utilized in determining the TEA and PCA, leading to a greater degree of subjectivity and variability in the determination of the AP axis. In certain conventional procedures, the AP axis is subjectively determined by an operator manually estimating or “eyeballing” the axis, a technique that may suffer from variability between the axes determined for a single model, whether by the same operator or different operators. For these reasons among others, there remains a need for further developments in this technological field.